The invention relates to an arrangement for controlling the rotational speed of an output rotational part of a fluid friction coupling, particularly a fan for cooling components of a motor vehicle which is coupled with a driving rotational part by way of a shearing fluid whose effective fluid quantity determines the transferrable torque. Arrangements of this type are used, for example, for controlling the rotational speed of a fan for cooling motor vehicle components, such as engines. In this case, the fan is coupled to the vehicle engine by way of the fluid friction coupling.
A rotational speed control arrangement of the above mentioned type for such an engine fan is described in the Journal Essay "Electronically Controlled Electromagnetic VISCO.RTM. Fan Clutches for Commercial Vehicles" by H. Martin, ATZ Automobiltechnische Zeitschrift, 1995, Vol. 5, No. 93, p. 3. The fan is used for providing a cooling air flow for diverse engine-related media, such as an engine coolant, charge air, engine oil, transmission oil and retarder oil. The fan is also used, as required, for the refrigerant of an air-condition system. The fan can be switched between four fan stages. The rotational control arrangement uses the engine coolant temperature and the charge air temperature as constant control quantities. These two types of temperature information are fed to two parallel temperature control units. From the two controller output signals as well as a retarder output signal, the signal corresponding to the highest fan stage is selected by way of an output stage and is fed as a drive signal to a solenoid. Together with a valve actuated by it, the solenoid operates as an adjusting unit for the variable adjusting of the effective amount of shearing fluid. For this purpose, the coupling has a storage chamber and a working chamber which encloses the rotational driving part in the form of a driven coupling disk and between which one inflow and one return flow, respectively, is provided for a shearing fluid circulation. This is caused by a circulation pump pumping the shearing fluid from the working chamber into the storage chamber. The valve, which can be actuated by the solenoid, controls the shearing fluid circulation and thus the quantity of shearing fluid which is, in each case, situated in the working chamber that is available as the effective fluid quantity for the transmission of the torque.
Fluid friction couplings with a timed electric driving of an adjusting unit for the variable adjusting of the effective shearing fluid quantity are also disclosed in European Patent Document EP 0 009 415 B1 and German Patent Document DE 44 41 808 A1.
The invention is based on the technical problem of providing a rotational speed control arrangement of the above mentioned type, which has an improved control action improved in comparison to the above-mentioned conventional arrangements.
The present invention solves this problem by providing a rotational speed control arrangement having an adjusting unit which can be electrically driven in a timed manner for variably adjusting the effective shearing fluid quantity. A temperature controller stage receives temperature information of one or several media whose temperature can be influenced by the output rotational speed. A rotational speed controller stage, which is connected behind the temperature controller stage, is fed with the output signal of the temperature controller stage as the desired output rotational speed information, as well as the actual output rotational speed information and the driving rotational speed information. The output signal of the rotation speed controller stage drives the shearing fluid quantity adjusting unit.
In the case of this arrangement, the temperature controller stage is followed by a rotational speed control stage that receives the output signal of the temperature controller stage as a desired output rotational speed information. In addition, the actual output rotational speed information and the driving rotational speed information are supplied to the rotational speed control stage. From the input information, the rotational speed controller stage generates, as the output signal, the drive timing signal. This output signal is supplied to the adjusting unit for the variable adjustment of the effective shearing fluid quantity. Using this construction of the control arrangement with a rotational speed control circuit and a temperature control circuit superimposed on the latter, in order to achieve the respective desired tempering effects, the temperature-influencing rotational speed of the rotational output parts of the coupling can be set comparatively precisely, sensitively and reliably.
In another embodiment of the arrangement, a chopping of the rectangular pulses of the output signal of the rotational speed controller stage is provided that is a function of the supply voltage for the shearing fluid quantity adjusting unit. As a result, the effective value of the voltage acting upon the adjusting unit can be maintained at a constant value. This is also true in the case of a varying supply voltage. The effect here is that the adjusting unit does not have to be designed for high fluctuations of the effective voltage.
In yet another embodiment, an arrangement is used for controlling the rotational speed of a fan for a motor vehicle engine. The temperature controller stage is designed such that, by means of filed characteristic diagrams, it determines, from the actual values of the rotational engine speed and the rotational torque suitable engine-operation-dependent, desired temperature values for one or several engine-related media to be tempered (e.g. the engine coolant, the charge air and/or the engine oil).
In a further embodiment, an arrangement further developed according to the temperature controller stage is designed in a special manner such that, for each rotational-speed-relevant input quantity, it has one rotational-speed demand unit, respectively. The units are situated in parallel to one another. From the rotational-speed demand signals supplied by these units, utilizing a maximal-value selection stage, the signal with the highest rotational speed demand will then be selected for the transmission as the desired output rotational speed signal for the rotational speed controller stage.
In a still further embodiment of the arrangement, the rotational speed controller stage is designed for obtaining, by means of a suitably filed characteristic slip effect diagram, slip effect information representing the coupling temperature from the supplied information concerning the actual output rotational speed and the driving rotational speed. By means of this information, it is capable of preventing, using corresponding control interventions and/or by the emission of a corresponding warning signal, the occurrence of excessively high coupling temperatures damaging the shearing fluid.
In another embodiment of the arrangement, the rotational speed controller stage is designed such that it obtains the drive timing signal for the shearing fluid quantity adjusting unit as the sum of a basic adjusting signal and of a correction adjusting signal. In this case, it determines the basic adjusting signal by means of a filed basic characteristic diagram as the function of the supplied information concerning the driving rotational speed and the desired output rotational speed. The correction signal supplies corrections which result particularly from deviations of the respective coupling from the ideal coupling action represented by the basic characteristic diagram.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.